Extracorporeal blood treatment apparatuses with a blood treatment unit through which a patient's blood flows are generally known. These include, for example, the known hemodialysis, hemofiltration or hemodiafiltration apparatuses. The known blood treatment apparatuses can be operated in the single-needle or double-needle operation.
With the single-needle operation, the blood is removed from the patient with a single needle, conveyed into the blood treatment unit of the blood treatment apparatus and fed back to the patient via a single needle. The blood removed from the patient is stored in a reservoir during an arterial phase and is fed back to the patient from the reservoir in a venous phase. The blood flows through the blood treatment unit of the blood treatment apparatus.
For the removal and return of the blood, use is made of replaceable blood hose systems with a blood supply line and blood return line, to which the single needle (cannula) is connected. The replaceable hose systems are put into the blood treatment apparatus and disposed of after the blood treatment. These hose systems are also referred to as disposables. The blood treatment unit is also generally intended for one-off use.
Blood treatment apparatuses for the single-needle operation are known which comprise only a single blood pump, which is disposed in the arterial blood supply line. For the collection of the blood, a blood reservoir which has a sufficient compliance is located upstream or downstream of the blood treatment unit. Apart from the blood treatment apparatuses for the single-needle operation with only a single blood pump, blood treatment apparatuses are also known which comprise two blood pumps, whereof one is disposed in the arterial blood supply line upstream of the blood reservoir and the other pump is disposed in the blood supply line leading to the blood treatment unit downstream of the blood reservoir. These two pumps are operated alternately in the arterial and venous phase. In the arterial phase, the blood removed from the patient is conveyed by the first blood pump into the blood reservoir, whilst in the venous phase the blood collected in the blood reservoir is conveyed to the patient by the second blood pump. The blood thereby flows through the dialyzer. It is crucial that the second blood pump is stationary during the operation of the first blood pump and that the first blood pump is stationary during the operation of the second blood pump. The blood supply line is therefore interrupted respectively upstream or downstream of the blood reservoir. A compliance of the blood reservoir is not required in the case of operation with two pumps.
Blood treatment apparatuses for the single-needle operation with one or two blood pumps are described for example in the specialist book “Replacement of Renal Function by Dialysis”, 5th Revised Edition, ISBN 1-4020-0083-9, Kluwer Academic Publishers pages 365-367.
A dialysis apparatus for the single-needle operation is known from German Patent Publication No. DE 196 33 657 C1, which comprises a blood pump disposed in the arterial blood line, the blood reservoir comprising a blood bag disposed in the arterial blood line and a blood bag disposed in the venous blood line. Pressure is applied with a device to both blood bags, so that blood can be conveyed out of the blood bags.
Small children and infants who are suffering from kidney failure are treated with only relatively small blood flows on account of their small body volume. Dialysis treatments with continuous blood flows which are relatively small, for example lying at approximately 5 ml/min, are generally not possible with blood treatment apparatuses comprising conventional blood pumps, since the internal control for the stabilization of the motor revolutions requires a defined minimum rotational speed for the pump rotor in order to guarantee a jerk-free operation. This results in a minimum blood flow of approx. 20 ml/min. This blood flow, however, is too great for patients with a low body weight, for example a body weight of 10 kg.
In view of the aforementioned problems, a goal underlying the present invention is to provide an apparatus for extracorporeal blood treatment in the single-needle operation, which also enables a blood treatment with relatively small blood flows.
A further goal of the present invention is to specify a method for extracorporeal blood treatment in the single-needle operation, which enables a blood treatment with relatively small blood flows.